1. Field of the Invention
The present invention relates to magnet-based sensors and in particular magnet-based sensors required for linear and rotary sensing.
2. Description of the Art
Magnetostrictive transducers having elongated waveguides that carry torsional strain waves induced in the waveguide when current pulses are applied along the waveguide through a magnetic field are well known in the art. A typical linear distance measuring device using a movable magnet that interacts with the waveguide when current pulses are provided along the waveguide is shown in U.S. Pat. No. 3,898,555.
Devices of the prior art of the sort shown in U.S. Pat. No. 3,898,555 also have the sensor element in a housing which also houses the electronics to at least generate the pulse and receive the return signal. The amplitude of the return signal detected from the acoustical strain pulse is, as well known in the art, affected by many parameters. These parameters include the position magnet strength, waveguide quality, temperature, waveguide interrogation current, and assembly tolerances.
Several types of magnetic-based sensors are available for measuring linear or rotary position. Magnetic-based sensors have an advantage in that they provide non-contact sensing; so there are no parts to wear out. Examples of magnetic-based sensors are LVDTs, inductive sleeve sensors, and magnetostrictive sensors.
It is an object of the present invention to combine the functions of a linear position sensor and rotary position sensor into one device.
It is another object of the present invention to provide a cost savings in applications that require both linear and rotary measurements, such as in measuring the gear selection in an automobile transmission.
It is yet another object of the present invention to sense rotary position using a linear position magnetostrictive sensor.
The present invention relates to a construction of a magnetostrictive linear and rotary position sensor, using at least two magnets. At least one magnet, the position magnet, is moved when measuring a linear motion. A second magnet moves in response to rotational motion about the waveguide or by a device in juxtaposition to the waveguide. This rotational motion can be measured with respect to a fixed position on the sensor, or with respect to the position magnet.
An alternate construction allows measuring rotary position sensing by using a linear position sensor with one or more magnets.